class BindBase1 {
public:
    int a = 42;
    double b = 11.7;
};

class BindTest1 : public BindBase1 {};

class BindBase2 {};

class BindTest2 : public BindBase2 {
public:
    int a = 42;
    double b = 11.7;
};

class BindBase3 {
public:
    int a = 42;
};

class BindTest3 : public BindBase3 {
public:
    double b = 11.7;
};

int main()
{
    BindTest1 bt1;
    BindTest2 bt2;
    BindTest3 bt3;
    auto[x1, y1] = bt1;    // 编译成功
    auto[x2, y2] = bt2;    // 编译成功
    auto[x3, y3] = bt3;    // 编译错误
}